Silicon wafers are widely used as a substrate material for semiconductor devices. Silicon wafers are manufactured by sequentially applying processes such as outer periphery grinding, slicing, lapping, etching, double-side polishing, single-side polishing, cleaning, etc., to a silicon single crystal ingot. Among the above processes, the single-side polishing process is a process required in order to remove unevenness or waviness of the wafer surface and thus to enhance flatness, in which mirror finishing by CMP (Chemical Mechanical Polishing) method is performed.
Typically, in the single-side polishing process for a silicon wafer, a single wafer polishing apparatus (CMP apparatus) is used. The wafer polishing apparatus includes a rotating platen to which a polishing cloth is affixed and a pressurizing head that holds a wafer on the rotating platen while pressing the wafer. The apparatus polishes one side of the wafer by rotating the rotating platen and pressurizing head while feeding slurry.
For example, as a technique for improving wafer machining accuracy, Patent Document 1 describes a method including measuring the temperature of a polishing cloth affixed onto the upper surface of a polishing rotating platen during machining by using a radiation thermometer and controlling the temperature of the polishing rotating platen to a constant temperature by supplying cooling water to a water-cooled jacket or shutting off the supply so that the temperature of the polishing cloth is kept constant. Further, Patent Document 2 describes a semiconductor wafer mirror polishing apparatus in which a measurement head of an eddy current displacement sensor that measures the displacement of a rotating platen in a non-contact manner is provided from the radial center of the rotating platen to the outer peripheral portion thereof. A method using the measurement head of the eddy current displacement sensor is advantageous over a method that estimates a change in the shape of the rotating platen from a temperature change calculated by measuring the temperature on a polishing pad using a radiation thermometer or by measuring the temperature of collected polishing solution in that there occurs no delay in measurement results and that the shape change of the rotating platen can be measured accurately.
Further, Patent Document 3 describes a polishing method that polishes an object to be machined while rotating a table provided with a polishing cloth by a motor. In this method, a torque current value for the motor during polishing is obtained for each section in accordance with a polishing process, and a polishing time for the object to be machined is determined based on a multiple regression formula in which the torque current value for each section is set as an explanatory variable. Further, Patent Document 4 describes a polishing method that determines a polishing end point of an object to be machined, such as a silicon substrate, based on an integrated value of drive current for rotating a rotating platen for polishing the object to be machined so as to detect the polishing end point reliably and speedily.